Micro-machined temperature dependent one-shot valve and process for production thereof

ABSTRACT

A micro-machined temperature dependent one-shot valve is provided which has an operation temperature adjustable readily, causing no leakage below the operation temperature even at a high pressure difference, being useful both in a liquid environment and in a gas environment, and being miniaturizable. The micro-machined temperature dependent one-shot valve comprises a silicon substrate  100 , a channel  101  penetrating the entire thickness of the silicon substrate, and a low melting point metal member  101  deposited on one face of the silicon substrate to obstruct the channel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro-machined temperature dependentone-shot valve, and to a process for production thereof. Morespecifically the present invention relates to a temperature dependentone-shot valve having a rupture mechanism, useful as a safety mechanismof a fuel cell, a feed-starting mechanism of a lab-on-a-chips, and asmart micro-pill, or a like mechanism. The present invention relatesalso to a process for producing the valve by a micro-machinetechnologies.

2. Description of the Related Art

Since 1980s, various micro-valves are disclosed which are produced bymicro-machine technologies (hereinafter referred to as “micro-machinedvalves”); (K. W. Oh, and C. H. Ahn: “A review of microvalves”, J.Micromech. Microeng., 16, R13-R39, 2006). According to the disclosures,the micro-machined valves are classified mainly into two groups: passivevalves and active valves.

On the other hand, another type of micro-machined valves are known whichare designed to function only once, such as one-shot valves. Theone-shot valves are useful, for example, as a valve for triggering amixing reaction in a lab-on-a-chips, and a valve for delivering amedical sample to a smart micro-pill. The one-shot valves, which areconstructed as a thermally operated valve, are useful as a safety valveof a fuel cell of a small portable device having a small fuel tank. Sucha valve can be applicable as a rupture mechanism for releasing thepressure when the pressure of the fuel cell rises abnormally owing to atemperature rise.

In the present invention, the one-shot valve which is manufactured by amicro-machine technologies and is operated by a temperature rise isdefined as a micro-machined temperature dependent one-shot valve.

A micro-machined temperature dependent one-shot valve is disclosed by O.Guerin, L. J. O. Dubochet, J.-F. Zeberli, Ph. Clot, and Ph. Renaud:“Miniature one-shot valve” IEEE MEMS Conference, pp. 425-428, 1998. Thisone-shot valve opens a obstructed micro-channel by melting of apolyethylene layer. Therefore, the operation temperature of this valvedepends on the melting temperature of the polyethylene.

Another micro-machined temperature dependent one-shot valve whichutilizes a micro-sphere is disclosed by P. Griss, Anderson H., and G.Stemme: “Expandable Microspheres for the Handling of Liquids”, Lab Chip,2:pp. 117-120, 2002. In this micro-machined temperature dependentone-shot valve, a micro-sphere held in a channel expands at or above apreset temperature to a volume of about 60 times the original volume toobstruct the channel. This micro-machined temperature dependent one-shotvalve serves to obstruct an release channel.

A still another micro-machined one-shot valve which is operated by anelectric current is disclosed by J. T. Santini, A. C. Richards, R.Scheidt, M. J. Cima, and R. Langer: “Microchips as ControlledDrug-Delivery Devices”, Angew. Chem. Int. Ed. 39, pp. 2396-2407, 2000.This valve is placed in a cell in a silicon wafer. At the top of thecell, a metal layer serving as an anode is deposited, and beside thecell another metal layer serving as a cathode is fusion bonded. Thisvalve is immersed in an electrolyte solution. Application of a potentialbetween the anode and the cathode oxidizes the anode and dissolves theanode in the electrolyte solution to open the valve.

Further, a thermal operation valve is disclosed in U.S. Pat. No.4,313,453. This valve is constituted of a sealing member composed of asolder placed at a metal tube connection portion. This solder stops theflow in the tube. Application of heat melts the solder to open the valveto allow the liquid to flow through the metal tube.

A safety device which prevents a damage of an atomic reactor pressurevessel is disclosed in U.S. Pat. No. 5,526,385. This device has a soldersealing at a pressure-compensation opening. In the normal operation, thesolder in a solid state seals the opening: an abnormally hightemperature melts the solder and the overpressure inside the reactorpushes out the melted solder to release the pressure.

The above-mentioned disclosed valves have disadvantages as below.

The one disclosed by O. Guerin et al. has its operation temperature notadjustable for its use, although the operation temperature of themicro-machined temperature dependent one-shot valve is preferablyadjustable arbitrarily to be suitable for the use. The desired operationtemperature of the valve depends on the boiling point of the liquid tobe handled, the maximum pressure of the gas in the container, and soforth.

For a pressure release, the stop valve should be capable of opening aflow path. However, the one disclosed by P. Griss et al. serves only toobstruct the flow path, but cannot release the flow path.

The one disclosed by J. T. Santini et al. is useful only in anelectrolyte environment, although the valve is preferably useful in anyuse environment as a safety mechanism or a feed-starting mechanism.

The micro-machined temperature dependent one-shot valve can beincorporated in a small system. Further it has advantages below. Oneadvantage is a high responsiveness to the environmental temperatureowing to rapid temperature diffusion in its small size of the valve.Another advantage is that the plural devices can be produced in a batchprocess on one and the same supporting member by a micro-machinetechnologies, especially an MEMS technique. This enables reduction ofthe production cost, and enables also simultaneous preparation of acontrol mechanism like a heater near the valve.

However, the one disclosed in U.S. Pat. Nos. 4,313,453 and 5,526,385employing a solder is produced necessarily by a typical macro-technique.Therefore the device cannot be made smaller in the size than 2-3 mm³,and the device cannot be produced by a batch process. Further, thecontrol system like a heater cannot be incorporated directly.

The problems with the micro-machined temperature dependent one-shotvalve are summarized as below.

At the ambient temperature higher than the preset temperature Tm, thepressure of the pressurized gas or liquid should be released. That is,the valve is designed such that the valve connected to a tank containinga pressurized gas or liquid is kept obstructed below the presettemperature, and opens at a temperature higher than the presettemperature. The temperature Tm of the valve opening should be madereadily adjustable in design of the system. The valve should keepobstructing against a large pressure difference at a temperature belowTm in a designed range without leakage.

The valve is useful both in a liquid environment and in a gasenvironment. Further, the valve is preferably formed in a size typicallysmaller than 2-3 mm³. The valve is preferably produced by a batchprocess. The valve can preferably be combined with a heater in thesystem for on-demand triggering of the valve.

LITERATURE LIST

-   1. D. H. Gracias, J. Tien, T. L. Breen, C. Hsu, and G. M.    Whitesides: “Forming Electrical Network in Three Dimensions by    Self-Assembly”, Science, 289, pp. 1170-1172, 2000-   2. “Material Safety Data Sheet of Indalloy Metal Mix Containing    Bismuth”, Indium Corporation of America-Europe-Asia-Pacific-   3. “Bismuth Alloys”, Small Parts Inc.,    http://www.smallparts.comm/products/descriptions/lma.cfm, 2006-   4. W. Zheng, and H. O. Jacobs: “Fabrication of Multicomponent    Microsystems by Directed Three Dimensional Self-Assembly”, Advanced    Functional Materials, 15, pp. 732-738, 2005-   5. H. Lorenz, M. Despont, N. Fahrni, N. LaBianca, P. Renau, and P.    Vettiger, “Su-8, a Low-Cost Negative Photo-Resist for MEMS”, J.    Micromech. Microeng., 7, pp. 121-124, 1997

SUMMARY OF THE INVENTION

The present invention intends to provide a micro-machined temperaturedependent one-shot valve having an operation temperature adjustablereadily, causing no leakage below the operation temperature even at ahigh pressure difference, being useful both in a liquid environment andin a gas environment, and being miniaturizable. The present inventionintends also to provide a process for producing the above micro-machinedtemperature dependent one-shot valve which may contain a heater in abatch production process.

The present invention is directed to a micro-machined temperaturedependent one-shot valve, comprising a silicon substrate, a channelpenetrating the entire thickness of the silicon substrate, a low meltingpoint metal member deposited on one face of the silicon substrate toobstruct the channel.

In the micro-machined temperature dependent one-shot valve, a metallayer can be provided between the low melting point metal member and thesilicon substrate. The metal layer can be formed from copper. Anadhesion layer can be provided between the metal layer and the siliconsubstrate. The adhesion layer can be a chromium layer or a titaniumlayer.

In the micro-machined temperature dependent one-shot valve, an adhesionlayer can be provided between the metal layer and the silicon substrate.The can be a chromium layer or a titanium layer.

The low melting point metal member can be formed from an alloycontaining at least one element selected from the group of Bi, Sn, Pb,In, and Cd.

In the micro-machined temperature dependent one-shot valve, a part ofthe low melting point metal member can be allowed to intrude into thechannel.

The metal layer composed of copper can be covered by a photoresistlayer, and a part of the low melting point metal member is allowed tointrude into the photoresist and is deposited to the metal layercomposed of copper.

In the micro-machined temperature dependent one-shot valve, a trench canbe formed on the portion of the silicon substrate onto which the lowmelting point metal member is deposited.

The surface of the low melting point metal member and the surface of thesilicon substrate onto which the low melting point metal member isdeposited can be covered at least partly by a photoresist.

In the micro-machined temperature dependent one-shot valve, a heatercomponent can be placed between the low melting point metal member andthe silicon substrate.

The present invention is directed to a process for producing amicro-machined temperature dependent one-shot valve comprised of achannel perforated through the entire thickness of a silicon substrate,and a low melting point metal member deposited on one face of thesilicon substrate to obstruct the channel, comprising the steps of:forming a channel through the entire thickness of the silicon substrate,and depositing the low melting point metal member on a face of thesilicon substrate to obstruct the channel.

The step of forming the channel can be conducted by reactive ionetching.

The step of forming the channel can be conducted by wet etching.

The patterning of the metal layer can comprise photolithography andmetal etching. The pattern formed by the patterning can have a circularshape.

The process for producing a micro-machined temperature dependentone-shot valve can comprise the steps of: depositing the low meltingpoint metal member, forcing a part of the low melting point metal memberto intrude into the channel by heating the silicon substrate up to atemperature higher than the melting temperature of the low-melting metaland applying a pressure difference between the both ends of the channel.

The process for producing a micro-machined temperature dependentone-shot valve can comprise the steps of: forming a trench on one faceof the silicon substrate, forming a channel to be adjacent to the trenchperforated through the entire thickness of the silicon substrate, anddepositing the low melting point metal member to cover the trench on thesilicon substrate and to obstruct the channel.

The process for producing a micro-machined temperature dependentone-shot valve can comprise the steps of: forming a metal layer on oneface of the silicon substrate, patterning the metal layer for formationof the low melting point metal member and for formation of a heatercomponent simultaneously, forming channel perforated through the entirethickness of the silicon substrate at the position where the metal layerhas been patterned for depositing of the low melting point metal member,and depositing the low melting point metal member on the patterned metallayer to obstruct the channel.

The present invention provides a micro-machined temperature dependentone-shot valve which has an operation temperature adjustable readily,causing no leakage below the operation temperature even at a highpressure difference, being useful both in liquid environment and in gasenvironment, and being miniaturizable. The present invention providesalso a process for producing the above micro-machined temperaturedependent one-shot valve which may contain a heater in a batchproduction process.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view for describing the micro-machinedtemperature dependent one-shot valve of First Embodiment of the presentinvention, and the process for production thereof.

FIG. 2 is a schematic sectional view for describing the micro-machinedtemperature dependent one-shot valve of Second Embodiment of the presentinvention, and the process for production thereof.

FIG. 3 is a schematic sectional view for describing the micro-machinedtemperature dependent one-shot valve of Third Embodiment of the presentinvention, and the process for production thereof.

FIG. 4 is a schematic sectional view for describing the micro-machinedtemperature dependent one-shot valve of Fourth Embodiment of the presentinvention, and the process for production thereof.

FIGS. 5A and 5B are drawings illustrate schematically the micro-machinedtemperature dependent one-shot valve of Fifth Embodiment of the presentinvention, and the process for production thereof. FIG. 5A is aschematic plan view, and FIG. 5B is a schematic sectional view.

FIGS. 6A and 6B illustrate states of the actual micro-machinedtemperature dependent one-shot valves. FIG. 6A is a top view of a valvein a obstructing state at a temperature below the valve operationtemperature. FIG. 6B is a top view of the valve opened by elevation ofthe ambient temperature and application of a pressure difference.

DESCRIPTION OF THE EMBODIMENTS

In the embodiments of the present invention, the micro-machinedtemperature dependent one-shot valve has a channel penetrating a siliconsubstrate through the entire thickness, and a low melting point metalmember deposited onto one face of the silicon substrate to obstruct thechannel.

The low melting point metal member changes its physical state (solid orliquid) depending on the temperature to change the mechanical strengthagainst the pressure applied from the channel side. The low meltingpoint metal member in a solid state obstructs the channel. The lowmelting point metal member, when it becomes liquid, is destructed torelease the channel.

The melting temperature of the low melting point metal member can beadjusted arbitrarily by selecting the metal composition. Specifically,the valve operation temperature can be adjusted precisely at intervalsof 2-3° C. in the range from 47° C. to several hundred degreescentigrade.

The pressure tolerance of the valve below the preset operationtemperature can be improved in any of the several methods below.

In one method, an adhesion layer and a metal layer are provided betweenthe low melting point metal member and the silicon substrate surface. Inanother method, the depositing area is increased by forming a trench onthe silicon substrate surface.

In still another method, the low melting point metal member is allowedto intrude into the channel formed through the silicon substrate toincrease the depositing strength. In still another method, the siliconsubstrate and the low melting point metal member depositing thereon arepartly covered with a photoresist to improve the bonding strength of thelow melting point metal member to withstand the inside pressure.

The micro-machined temperature dependent one-shot valve of the aboveconstitution can be positively operated by a heater attached to thevalve, not only by change of the ambient temperature.

The one-shot valve of the above constitution is useful as a releasemechanism for a gas or a liquid.

According to the process for production of the present invention, themicro-machined temperature dependent one-shot valve can be produced in asize typically of smaller than 2-3 mm³. The smaller size of temperaturedependent one-shot valve is highly sensitive to the ambient temperatureas mentioned above to enable precise fine-tuning of the operationtemperature. The valve can be produced in a batch process, which enablesreduction of the production cost, and enables also simplification ofinstallation of the heater by simultaneous fabrication.

The present invention is described below specifically by reference todrawings.

First Embodiment

The micro-machined temperature dependent one-shot valve and a productionthereof of the present invention are described below.

FIG. 1 is a sectional view for describing the micro-machined temperaturedependent one-shot valve and the process for production thereof. Themicro-machined temperature dependent one-shot valve of this Embodimentis constituted of channel 101 penetrating through silicon substrate 100,and metal member 102 deposited to obstruct the one end of channel 101.

A process for producing the micro-machined temperature dependentone-shot valve is described below.

Firstly, a mask for deep RIE (reactive ion etching) for forming thechannel is formed on the back face of silicon substrate 100. When pluralvalves for the channels are produced in a batch process, the mask isformed to fit to the prescribed positions of individual channels 101.The mask is preferably solvent-resistant, and may be formed fromaluminum, silicon dioxide, or a like material.

On the front face reverse to the masked face of silicon substrate 100,adhesion layer 104 is formed from chromium, and metal layer 103 isformed from copper (hereinafter referred to as “a copper layer”). Thelayers are patterned. The layers may be formed by sputtering not to forma pinhole. The patterning may be conducted either by photolithographyand metal etching, or by a lift-off process. This pattern is formed alsoto fit to the prescribed positions of the individual valves to be formedon one substrate.

With the mask which has been formed preliminarily on the back face ofsubstrate 100, silicon substrate 100 is etched by deep RIE to perforatechannels 101 through silicon substrate 100. In this etching, metal layer103 and adhesion layer 104 are not etched so that channel 101 is keptobstructed at the front side end.

Next, silicon substrate 100 is immersed in a two-phase liquid bathcontaining a fused low-melting metal as the lower phase and a dilutehydrochloric acid solution of pH 1 as the upper phase. This method isdescribed in detail in Literature-1 shown later in the literature list.Incidentally, Literature 2-4 cited in the description below are alsocontained in the literature list. At first, natural copper oxide on thecopper layer surface is etched by the dilute hydrochloric acid, whereasthe oxide layer on the surface of the aluminum layer is not etched bythe dilute hydrochloric acid. Since the interfacial energy between thewater and the copper is higher than that between the low-melting metaland the copper, the copper layer is coated with the low-melting metal.On the other hand, the interface energy between water and othersubstance (aluminum oxide, silicon dioxide, and silicon) is lower thanthat between the low-melting metal and the above-mentioned substance.Therefore, the substance is not coated with the low-melting metal, butlow melting point metal member 102 deposits selectively by depositing onmetal layer 103 as shown in FIG. 1.

Finally, plural valves prepared on one substrate are separated bycutting in a prescribed size. In use of this valve, the positivepressure is applied from inside channel 101 against the valve, namelylow melting point metal member 102.

The melting temperature of the low-melting metal employed preferably inthe present invention is described briefly below. The meltingtemperature depends on the composition of the material of thelow-melting metal. The data below are cited from Literature-2 andLiterature-3.

A low-melting metal composed of Bi (44.7%), Pb (22.6%), Sn (8.3%), Cd(5.3%), and In (19.1%) has the melting temperature at 47° C. This is anexample of an extremely low melting temperature. A change of thecomposition of the above low-melting metal to Bi (44.7%), Pb (22.6%), Sn(11.3%), Cd (5.3%), and In (16.1%) raises the melting temperature to 52°C. Thus a slight change of the composition changes the meltingtemperature of the low-melting metal slightly.

A higher melting temperature can be obtained by adjusting thecomposition of the metal. For example, a metal composed of Bi (33.33%),Sn (33.33%) and Pb (33.34%) has the melting point at 143° C. On theother hand, a metal composed of Bi (60%) and Cd (40%) has the meltingpoint at 144° C.

Metals following the RoHS direction (lead-free and cadmium-free) arealso applicable as the low-melting metal. For example, a metal composedof Bi (32.5%), Sn (16.5%), and In (51%) has the melting point at 60° C.A metal composed of Bi (5%), and In (95%) has the melting point at 150°C. Metallic Bi (100%) has the melting point at 271° C. Thus within thescope of the RoHS direction, a broad range of melting temperatures canbe obtained.

When the melting temperature of the low-melting metal is higher than theboiling temperature (100° C.) of water, the water in the two-phaseliquid bath is replaced by ethylene glycol (boiling point: 19° C.) ortetraethylene glycol (boiling point: 328° C.), (Literature-4).

Depending on the situation, instead of the deep RIE, channel 101 may beformed by wet etching by use of KOH or TMAH, a conventionalsilicon-etching solution. With KOH, the mask on the back face ofsubstrate 100 may be formed from silicon nitride, and With TMAH, themask may be formed from silicon dioxide. During the etching from theback face, the front face of substrate 100 is protected by a usualprotection method like coverage with Teflon®.

Silicon can be etched at a much lower cost by wet etching than that bydeep RIE. However, the pattern formed by the wet etching is usuallyrectangular in the shape and is aligned on the crystal face of thesilicon substrate. In the rectangular pattern, mechanical stressconcentrates at the right angles of the rectangular patterndisadvantageously. The mechanical stress accumulated during formation ofmetal layer 103 can break metal layer 103 in coating with thelow-melting metal.

The deep RIE, on the other hand, can form any shape of pattern. Acircular pattern formed thereby is less liable to cause breakage ofmetal layer 103.

When the low-melting metal is allowed to intrude into channel 101, thelow-melting metal can not readily intrude the right angle of channel 101having a rectangular cross-section. In this case also, the deep RIE witha circular pattern is preferred.

In some uses, the adhesion force of low melting point metal member 102to silicon substrate 100 can be insufficient to cause separation of lowmelting point metal member 102 from silicon substrate 100 below themelting temperature of the low-melting metal to open the valve. Theadhesion force of low melting point metal member 102 to siliconsubstrate 100 can be increased as described below. The low-melting metalis heated up to a temperature higher than its melting temperature, andin this state a controlled pressure is applied against the low-meltingmetal 102 toward the channel 101 to allow a part of the meltedlow-melting metal to intrude into channel 101. Then the low-meltingmetal in a melted state is cooled with the pressure difference keptretained. Thereby the low-melting metal becomes solidified at thatposition. The intrusion of a part of the low-melting metal into channel101 increases the contact area between silicon substrate 100 and lowmelting point metal member 102. Moreover, the interface of the increasedarea of contact is directed to be parallel to the force applied to thelow-melting metal in usual operation conditions. The strength of bondingof the low-melting metal with silicon substrate 100 at the channel wallagainst the shear force is higher than that perpendicular at the outsideface of silicon substrate 100. The pressure for intrusion of a part ofthe low-melting metal into channel 101 may be applied either by a liquidor by a gas, and can readily be controlled by a pressure regulator. Thepressure may be applied in the batch process to plural valves formed ona substrate, and the valves may be separated into individual valves.

FIGS. 6A and 6B illustrate actually prepared micro-machined temperaturedependent one-shot valves of the present invention. FIG. 6A is a topview of a valve in a obstructing state below the temperature of thevalve operation. In FIG. 6A, the nearly square black-color portionindicates the low melting point metal member. FIG. 6B illustrates anopened valve which has been opened by elevating the ambient temperatureand applying a pressure difference: the low melting point metal memberis removed and the channel (the black circular portion at the center) isreleased. In the example of FIGS. 6A and 6B, the low-melting metal had amelting point of 47° C., and a pressure difference of 2.5 atmosphereswas applied. This valve came to open at about 49° C.

Second Embodiment

In another type of micro-machined temperature dependent one-shot valveand a process of production thereof are described in this Embodiment.FIG. 2 is a sectional view for describing the micro-machined temperaturedependent one-shot valve and the process for production thereof. In FIG.2, the same symbols as in FIG. 1 are used for denoting the correspondingmembers.

This Embodiment is different from First Embodiment in that, in theprocess of coating with the low-melting metal, only the uncovered coppersurface portion is coated with the low-melting metal by immersion in thetwo-phase liquid bath containing the melted low-melting metal.

In this Embodiment, as illustrated in FIG. 2, adhesion layer 104 formedfrom chromium and metal layer 103 formed from copper are not patterned,which is different from First Embodiment. The upper layer of copper iscovered with photoresist layer 200. The photoresist is patterned byphotolithography to bare only the portion of the copper surface to becoated with the low-melting metal. By immersion of substrate 100 in theliquid bath containing the melted low-melting metal, the bared portiononly of the copper surface is coated with the low-melting metal. Thesurface of photoresist layer 200 will not be coated by the low-meltingmetal similarly as aluminum oxide, silicon, and silicon dioxide.

The production process of this Embodiment is simpler than that ofEmbodiment 1, since metal layer 103 is not patterned. Therefore, in theprocess of the present invention, the metal etching or photoresistpeeling like a lift-off treatment is not necessary at all. Further, thelarger area of metal layer 103 can prevent leakage through the boundarybetween chromium adhesion layer 104 and the upper face of siliconsubstrate 100. In particular, for use of a gas of a small mass likehydrogen in the system such as a fuel cell, the prevention of the gasleakage is important.

This Embodiment is preferred when the valve use environment is notlimited by the heat-resistance, chemical stability, mechanicalproperties, and other properties of the photoresist.

Third Embodiment

The micro-machined temperature dependent one-shot valve in thisEmbodiment has a trench for stronger adhesion of the low melting pointmetal member to the substrate and for improved sealing of the valve.FIG. 3 is a sectional view for describing the micro-machined temperaturedependent one-shot valve and the process for production thereof. In FIG.3, the same symbols as in FIG. 1 are used for denoting the correspondingmembers.

This Embodiment intends to improve the adhesion of low melting pointmetal member 102 to silicon substrate 100, and to improve the sealing ofthe valve. For the above purposes, before formation of the chromiumlayer and the copper layer, trench 300 is provided on the surface ofsilicon substrate 100. This trench 300 can be formed by a conventionaltechnique including masking, photolithography, and silicon etching. Theother production steps basically are the same as in First Embodiment andSecond Embodiment. When the wall face of trench 300 is nearlyperpendicular to substrate 100 and the chromium layer and the copperlayer are vapor-deposited by sputtering, the perpendicular wall face oftrench 300 is coated with the metal layers. Therefore, in the process ofthe low-melting metal coating, low melting point metal member 102intrudes into trench 300.

FIG. 3 illustrates trench 300 formed in the valve of Second Embodimentof the present invention. Trench 300 may be formed also in the valve ofFirst Embodiment of the present invention.

The formation of trench 300 increases the contact area between lowmelting point metal member 102 and metal layer 103. This increase of thecontact area strengthens the adhesion between low melting point metalmember 102 and silicon substrate 100.

When the wall of trench 300 is formed nearly perpendicular to siliconsubstrate 100, the pressure difference at valve 102 causes a shearingforce between low melting point metal member 102 and the wall of thetrench 300. This partial intrusion of the low-melting metal into trench300 strengthens the adhesion between low melting point metal member 102and silicon substrate 100, similarly as in First Embodiment in which thelow-melting metal is allowed to intrude into the channel.

Further, the sealing of the valve can be improved by selecting the shapeof trench 300. Trench 300 surrounds channel 101 and is obstructed. Thepath for leakage of the fluid from channel 101 through trench 300 to theside of the valve is twisted, whereby the sealing is improved.Incidentally, the number of trenches 300 is not limited to thatillustrated in FIG. 3. For further improvement of the bonding strengthof low melting point metal member 102, the multiple trenches may beformed on the substrate surface.

Fourth Embodiment

The micro-machined temperature dependent one-shot valve of this FourthEmbodiment has a photoresist applied and patterned to improve theadhesion between low melting point metal member and the siliconsubstrate.

FIG. 4 is a sectional view for describing the micro-machined temperaturedependent one-shot valve and the process for production thereof. In FIG.4, the same symbols as in FIG. 1 are used for denoting the correspondingmembers.

This Embodiment intends to improve not only the sealing of the valve butalso to improve adhesion of low melting point metal member 102. The twoimprovements can be achieved by a simple formation step. After theproduction process described in any of the above Embodiments,photoresist layer 400 is formed on the face of the valve, and patternedby photolithography.

FIG. 4 illustrates application of the photoresist layer to FirstEmbodiment. Photoresist layer 400 is patterned to cover the surface ofthe valve except the center portion of low melting point metal member102. The opening portion may be in the shape of a disk, or may be in anyother shape.

The contact area of between photoresist layer 400 and silicon substrate100 is larger than that between low melting point metal member 102 andsilicon substrate 100. Therefore, the adhesion force of photoresist 400to silicon substrate 100 is stronger than the adhesion force between lowmelting point metal member 102 and silicon substrate 100. Further,photoresist 400 covers a part of low melting point metal member 102.This contributes to the increase of the adhesion force between lowmelting point metal member 102 and silicon substrate 100.

The path of possible leakage along the interface between siliconsubstrate 100 and chromium adhesion layer 104 is made longer byphotoresist layer 400. This elongation of the leakage path improves thesealing.

The material of photoresist 400 of this Embodiment may be selected to besuitable for intended use of the valve. For example, Su-8, aphotosensitive material for an epoxy-based, is suitable as a materialfor photoresist layer 400 since Su-8 is resistant against varioussolvents and acids (Literature-5). Otherwise a solvent-resistantphotoresist like a OMR photoresist is useful.

Fifth Embodiment

The micro-machined temperature dependent one-shot valve of thisEmbodiment has a micro-heater inside the valve for on-demand triggeringof opening the one-shot valve.

FIG. 5A is a schematic plan view of the micro-machined temperaturedependent one-shot valve of this Embodiment. FIG. 5B is a schematicsectional view for describing the production process of the valve. InFIGS. 5A and 5B, the same symbols as in FIG. 1 are used for denoting thecorresponding members.

In this Embodiment, a micro-heater is incorporated in the valve. Themicro-heater is constituted of micro-resistor 501 placed between lowmelting point metal member 102 and substrate 100, and two electrode pads500 connected electrically to micro-resistor 501. Micro-heater 501placed under low melting point metal member 102 serves alsosubstantially as metal layer 103. Application of an electric currentfrom electrode pads 500 through micro-resistor 501 raises thetemperature of the micro-heater to heat low melting point metal member102. When the low-melting metal has been heated to a melting temperatureof the low-melting metal, the valve is opened by the pressure differencebetween the both sides of the valve. Thus the valve can be opened asnecessary by application of the electric current. The valve operated byapplication of an electric current to the heater can serve as a safetyvalve for an explosive gas or liquid on accidental temperature rise byadjusting the melting temperature of the low-melting metal by changingthe composition of the low-melting metal.

The process for production of the valve of this Embodiment is basicallythe same as that of First Embodiment. In this Embodiment, in patterningof the chromium layer and the copper layer, the patterns ofmicro-resistor 501 and electrode pads 500 are formed simultaneously withthe pattern for coating of low melting point metal member 102. Beforethe immersion of substrate 100 in the liquid bath for coating with lowmelting point metal member 102, micro-resistor 500 and electrode pads501 are preferably coated preliminarily with a photoresist not to becoated by the low-melting metal.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-305353, filed Nov. 10, 2006, which is hereby incorporated byreference herein in its entirety.

1. A valve, comprising: a planar crystal substrate; a channelpenetrating an entire thickness of the planar crystal substrate; and alow melting point metal member deposited on one face of the planarcrystal substrate to obstruct the channel.
 2. The valve according toclaim 1, wherein a metal layer is provided between the low melting pointmetal member and the planar crystal substrate so as to obstruct thechannel. 3-5. (canceled)
 6. The valve according to claim 1, wherein thelow melting point metal member is formed from an alloy containing atleast one element selected from a group that includes: Bi, Sn, Pb, In,and Cd.
 7. The valve according to claim 1, wherein a part of the lowmelting point metal member is allowed to intrude into the channel. 8.The valve according to claim 2, wherein the metal layer formed fromcopper is covered by a photoresist layer, and a part of the low meltingpoint metal member is allowed to intrude into the photoresist layer andis deposited on the metal layer formed from copper.
 9. The valveaccording to claim 1, wherein a trench is formed on a portion of theplanar crystal substrate onto which the low melting point metal memberis deposited.
 10. (canceled)
 11. The valve according to claim 1, whereina heater component is placed between the low melting point metal memberand the planar crystal substrate.
 12. A process for producing a valvecomprised of a channel perforated through an entire thickness of aplanar crystal substrate, and a low melting point metal member depositedon one face of the planar crystal substrate to obstruct the channel, theprocess comprising steps of: forming a channel through an entirethickness of a planar crystal substrate; and depositing a low meltingpoint metal member on a face of the planar crystal substrate to obstructthe channel.
 13. The process for producing a valve according to claim12, wherein the step of forming the channel is conducted by reactive ionetching.
 14. The process for producing a valve according to claim 12,wherein the step of forming the channel is conducted by wet etching. 15.The process for producing a valve according to claim 12, wherein thestep of depositing the low melting point metal member is conducted byimmersing the planar crystal substrate in a two-phase liquid bath thatincludes a low-melting metal as one of the two liquid phases.
 16. Theprocess for producing a valve according to claim 12, further comprisingsteps of: forming a metal layer on one face of the planar crystalsubstrate; patterning the metal layer; forming the channel perforatedthrough the entire thickness of the planar crystal substrate at aposition where the metal layer has been patterned; and depositing thelow melting point metal member on the metal layer to obstruct thechannel.
 17. The process for producing a valve according to claim 12,wherein the depositing the low melting point metal member includesforcing a part of the low melting point metal member to intrude into thechannel by heating the planar crystal substrate up to a temperaturehigher than the melting temperature of the low-melting metal andapplying a pressure difference between both ends of the channel.
 18. Theprocess for producing a valve according to claim 12, further comprisingsteps of: forming a trench on one face of the planar crystal substrate;forming the channel to be adjacent to the trench perforated through theentire thickness of the planar crystal substrate; and depositing the lowmelting point metal member to cover the trench on the planar crystalsubstrate and to obstruct the channel.
 19. The process for producing avalve according to claim 12, further comprising steps of: forming ametal layer on one face of the planar crystal substrate; patterning themetal layer for formation of the low melting point metal member and forformation of a heater component simultaneously; forming the channelperforated through the entire thickness of the planar crystal substrateat a position where the metal layer has been patterned for thedepositing of the low melting point metal member; and depositing the lowmelting point metal member on the patterned metal layer to obstruct thechannel.